Why does a laptop screen jump

Make sure you are not near strong electromagnetic fields, badly shielded power lines in the wall, other monitors near the laptop, things like that. Maybe some speakers that are not well made near the screen.

Are you serious hang-the-9? You just don't get it do you?
Shellz I'm having the same problem too.
It happens when I install SP2 on Vista, on my PC and laptop.
On another page of advice I read that it doesn't happen when you open Firefox with Ctrl+N.
So far this works but it happens with Word 2007 as well!
Any ideas?

I don't get what? Without any details as to exactly what is going on and when, screen "jumping" "shuddering" etc... can be caused by outside interference. And you should not tack on to other people's posts but start a new one. And add details about how exactly the screen "jumps".